Synthesis, spectral, and computational studies of some energetic picrates

Article abstract of DOI:10.1016/j.molstruc.2019.05.018

This work discusses the synthesis and characterization of some of the thermodynamically stable energetic materials of c(3),t(3)-dimethyl-r(2),c(6)-diarylpiperidin-4-one picrates which are the analogues of the explosive D “The Dunnite”. c(3),t(3)-Dimethyl-

Full text of DOI:10.1016/j.molstruc.2019.05.018

Accepted Manuscript
Synthesis, spectral, and computational studies of some energetic picrates
Kannan Gajendran Balachandar, Arumugam Thangamani
PII:
S0022-2860(19)30572-1
DOI:
https://doi.org/10.1016/j.molstruc.2019.05.018
MOLSTR 26525
Reference:
To appear in: Journal of Molecular Structure
Received Date: 27 February 2019
Revised Date: 5 May 2019
Accepted Date: 7 May 2019
Please cite this article as: K.G. Balachandar, A. Thangamani, Synthesis, spectral, and computational
studies of some energetic picrates, Journal of Molecular Structure (2019), doi: https://doi.org/10.1016/
j.molstruc.2019.05.018.
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ACCEPTED MANUSCRIPT
Graphical Abstract
CH3
O
O
C
CH3
CH3
H3C
CHO
R
CHO
CH3
N
O
H
H
+
R
R
NH4OAc
O2N
NO2
R
NO2

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ACCEPTED MANUSCRIPT
Journal Name
:
:
Journal of Molecular Structure
Title of the Article
Synthesis, Spectral, and Computational Studies of some
Energetic Picrates
Total Number of Pages
Number of Tables
:
:
27
05
Number of Figures
Corresponding Author
:
05 (including Scheme)
:
Dr. A.Thangamani
Associate Professor
Department of Chemistry
Karpagam Academy of Higher Education,
Coimbatore- 641 021
Tamil Nadu, India.
Mobile No.: + 91 9345496093
E-mail: thangabell2003@yahoo.co.in;
thangabell2003@gmail.com

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Synthesis, Spectral, and Computational Studies of some
Energetic Picrates
Kannan Gajendran Balachandar, Arumugam Thangamani*
Department of Chemistry, Karpagam Academy of Higher Education, Coimbatore-641021,
Tamil Nadu, India.
___________________________________________________________________________
ABSTRACT
This work discusses the synthesis and characterization of some of the
thermodynamically stable energetic materials of c(3),t(3)-dimethyl-r(2),c(6)-diarylpiperidin-
4-one picrates which are the analogs of the explosive D “The Dunnite”. c(3),t(3)-Dimethyl-
r(2),c(6)-diarylpiperidin-4-one picrates have been synthesized by reacting c(3),t(3)-dimethyl-
r(2),c(6)-diarylpiperidin-4-ones with picric acid in ethanol medium at room temperature.
1
13
Spectral methods like IR, H NMR and C NMR were used to characterize the synthesized
compounds. Subsequently the explosive properties of the synthesized compounds were
studied with the standard equations and compared with that of LOTUSES code simulated
results. The calculated physiochemical properties of these energetic materials are compared
with that of picric acid and Dunnite. The addition of piperidone moiety into picric acid helps
in controlling and mitigating the risk of the hazardous nature of the energetic materials.
Keywords: IR, NMR, Oxygen balance, Crystal density, Detonation velocity, LOTUSES code
*Corresponding author.
E-mail address:thangabell2003@gmail.com (Arumugam Thangamani)
1. Introduction
Generally, thermally stable energetic materials are invariably used for civilian and
military explosive applications. So, researchers are in search of green and thermally stable
energetic materials, as they are safer to produce, have longer shelf life, low vulnerability to
accidental ignition and are cost-effective. Picrates and explosive D are stable explosives, and
Dunnite was the first explosive used by Italians in aerial bombings as it could withstand an
enormous amount of pressure. The basic criteria for an explosive are that it should contain

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least carbon and hydrogen atoms and more nitrogen and oxygen atoms. A few exceptions are
Akradite-I (diphenyl urea C13H12N2O), Akradite-II (methyl diphenyl urea, C14H14N2O),
Centralite III (ethyl methyl urea C16H18N2O), Centralite II (dimethyl diphenyl urea
C15H16N2O), Centralite I (ethyl methyl urea C17H20N2O), which have less nitrogen and
oxygen atoms [1].
Picric acid, being acidic in nature forms crystalline picrate salts through hydrogen
bonding or by specific electrostatic interaction. The bond formation process in picric acid
complexes is due to the strength and nature of electron donor–acceptor type bonding. The
linkage involves the formation of molecular complexes and electrostatic interactions. With
aromatic compounds, picric acid acts as an acceptor to form various pi-stacking complexes
and also as an acidic ligand to form stable salts by means of hydrogen bonding or electrostatic
interactions. During the formation of conjugated base, the picrates, the value of molecular
hyper polarizibility is increased due to proton transfer [2].
Picric acid plays a pivotal role in the production of very sensitive compounds due to
the presence of three nitro groups, which are powerful oxidizing agents that decompose and
explode at higher temperatures. A proton transfer mechanism is the primary step in thermal
decomposition, which is an attractive part in the study of the explosive properties of energetic
picrates [3].
Picrates are explosives. Some are primary explosives. The interesting parts of picrates
are their low cost, ultrafast response, hydrogen bonding, aromatic–aromatic interactions etc.
Hetero aromatic nitro compounds perform well when compared to their analogous aromatic
systems. It is a proven fact that density increases when a picryl group is introduced into an
organic compound. It is also reported that it increases the insensitivity and the thermal
stability of the molecule [4].
Picric acid forms crystalline picrates with various organic molecules through non-
covalent, ionic and pi-pi interactions, as they are extensively used as supramolecular
heterosynthon in co-crystals designing. In such cases, picric acid acts not only as an acceptor
but also as a ligand. In this co-crystallisation work, the piperidone nucleus, which is both
thermally and hydrolytically stable, renders thermal stability to the synthesized compounds
and also decreases the explosive properties [5].

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Acid-base complexes, based on strong directional hydrogen bonding, are the main
driving force behind the design of supramolecular solids. They have different properties and
potential applications as functional materials. The secondary component synthesized here is
an N-heterocyclic base, which has a higher heat of formation, oxygen balance and density,
than carbocyclic analogues, and is involved in hydrogen bonding with picric acid [6].
Based on the above aspects, the present work is on synthesis, spectral, and
computational studies of c(3),t(3)-dimethyl-r(2),c(6)-diarylpiperidin-4-one picrates.
Explosive properties such as core crystal density, condensed phase heat of formation, oxygen
balance, detonation temperature, heat of detonation, detonation velocity or velocity of
detonation (VoD), detonation pressure, impact sensitivity, gurney energy, explosive power
and power index of the synthesized compounds are calculated and compared with those of the
reference
materials
like
picric
acid
and
Dunnite.
2. Experimental
2.1. Materials and methods
Ammonium acetate, various substituted benzaldehydes, isopropyl methyl ketone,
picric acid, and ethanol were purchased from Sigma Aldrich, Bengaluru, India. The open
capillary method was used to record the melting point. Avatar–370 FT-IR spectrometer using
1
KBr (pellet form) was used to record the IR spectra. H NMR spectra were recorded at 400
MHz and 13C NMR spectra at 100 MHz on a Bruker Avance III using DMSO-d6 as solvent,
which is normally used to determine the spectral studies. Tetramethylsilane (TMS) was used
as reference for NMR spectra. All NMR measurements were made on 5 mm NMR tubes.
The spectral parameters for 1H were as follows: spectral width 8223.685 Hz, acquisition time
3.9846 s, number of data points 32768, digital resolution 0.3 Hz, and number of scans 64. For
13C the spectral parameters were as follows: spectral width 24038.461 Hz, acquisition time
1.3632 s, number of data points 65536, digital resolution 1.0 Hz, and number of scans 1024.
1H NMR splitting patterns are designated as singlet (s), broad singlet (br s), doublet (d), broad
doublet (br d), doublet of doublet (dd), triplet (t), and multiplet (m).

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2.2. General procedure for the synthesis of c(3), t(3)-dimethyl-r(2),c(6)-diarylpiperidine-4-
one picrates (1-7)
The c(3),t(3)-dimethyl-r(2),c(6)-diarylpiperidin-4-ones were obtained by the double
Mannich condensation of various substituted benzaldehydes, ammonium acetate, and
isopropyl methyl ketone in the molar ratio of 2:1:1 in ethanol medium at warm conditions,
and kept at room temperature for 4 to 6 hrs to solidify and filter them. The c(3),t(3)-dimethyl-
r(2),c(6)-diarylpiperidine-4-one picrates 1-7 were prepared by mixing equimolar solution of
c(3),t(3)-dimethyl-r(2),c(6)-diarylpiperidin-4-ones (20 mmol) in ethanol with picric acid
(20 mmol) in ethanol and continuously stirring the solution for 40 min. A yellow powder
was formed, filtered and dried.
2.2.1. c(3),t(3)-Dimethyl-r(2),c(6)-diphenylpiperidin-4-one picrate (1)
Yield: 82%. m.p. 158-160°C; IR (KBr) (cm-1): 3175 (aromatic C-H), 1719 (C=O),
1609 (C=C), 1568 (NO2 asymmetric), 1437 (C-O), 1319 (NO2 symmetric), 1160 (C-N);
1H NMR (DMSO-d6, 400 MHz): δ (ppm): 10.23 (br s, 1H, Eq-NH), 9.40 (br s, 1H, Ax-NH),
8.60 (s, 2H, picryl ring), 7.65-7.63 (m, 2H, Ar-H), 7.53-7.48 (m, 8H, Ar-H), 4.99 (br d, 1H,
J = 12.0 Hz, H-6), 4.87 (br s, 1H, H-2), 3.64 (t, 1H, J = 14.6 Hz, H5a), 2.74 (dd, 1H, J = 15.4
& 2.2 Hz, H5e), 1.21 (s, 3H, CH3), 0.94 (s, 3H, CH3); 13C NMR (DMSO-d6, 100 MHz):
δ (ppm): 206.13 (C=O), 160.82 (C-O), 141.79, 129.64, 129.03, 128.70, 128.55, 128.29,
125.18, 124.29, 66.46 (C-2), 58.29 (C-6), 47.42 (C-5), 20.74 (CH3), 19.67 (CH3).
2.2.2. c(3),t(3)-Dimethyl-r(2),c(6)-di(4-fluorophenyl)phenylpiperidin-4-one picrate (2)
Yield: 79%. m.p. 141-143°C; IR (KBr) (cm-1): 3075 (aromatic C-H), 1725 (C=O),
1608 (C=C), 1560 (NO2 asymmetric), 1435 (C-O), 1318 (NO2 symmetric), 1161 (C-N);
1H NMR (DMSO-d6, 400 MHz): δ (ppm): 10.19 (br s, 1H, Eq-NH), 9.43 (br s, 1H, Ax-NH),
8.60 (s, 2H, picryl ring), 7.70-7.67 (m, 2H, Ar-H), 7.58-7.54 (m, 2H, Ar-H), 7.35-7.29
(m, 4H, Ar-H), 4.98 (d, 1H, J = 12.8 Hz, H-6), 4.87 (br s, 1H, H-2), 3.64 (t, 1H, J = 14.6 Hz,
H5a), 2.72 (dd, 1H, J = 15.6 & 2.8 Hz, H5e), 1.21 (s, 3H, CH3), 0.93 (s, 3H, CH3); 13C NMR
(DMSO-d6, 100 MHz): δ (ppm): 206.19 (C=O), 162.65 (d, JCF = 245.4 Hz), 162.31
(d, JCF = 244.7 Hz), 160.83 (C-O), 141.73, 131.24 (d, JCF = 7.9 Hz), 131.12, 125.21, 124.48,
115.38 (d, JCF = 21.5 Hz), 115.22 (d, JCF = 21.5 Hz), 65.74 (C-2), 57.67 (C-6), 47.45 (C-5),
20.60 (CH3), 19.54 (CH3).

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2.2.3. c(3),t(3)-Dimethyl-r(2),c(6)-di(4-chlorophenyl)phenylpiperidin-4-one picrate (3)
Yield: 86%. m.p. 148-150°C; IR (KBr) (cm-1): 3092 (aromatic C-H), 1723 (C=O),
1611 (C=C), 1563 (NO2 asymmetric), 1439 (C-O), 1317 (NO2 symmetric), 1085 (C-N);
1H NMR (DMSO-d6, 400 MHz): δ (ppm): 9.59 (br s, 1H, Eq-NH), 9.56 (br s, 1H, Ax-NH),
8.59 (s, 2H, picryl ring), 7.64 (d, 2H, J = 8.4 Hz, Ar-H), 7.57-7.48 (m, 6H, Ar-H), 4.96 (d,
1H, J = 12.4 Hz, H-6), 4.84 (s, 1H, H-2), 3.61 (d, 1H, J = 14.8 Hz, H5a), 2.73 (dd, 1H,
13
J = 15.4 & 3.0 Hz, H5e), 1.19 (s, 3H, CH3), 0.93 (s, 3H, CH3); C NMR (DMSO-d6, 100
MHz): δ (ppm): 211.34 (C=O), 166.08 (C-O), 146.97, 139.60, 139.11, 136.11, 135.87,
133.78, 133.58, 130.47, 129.71, 71.09 (C-2), 62.96 (C-6), 52.65 (C-5), 25.83 (CH3), 24.79
(CH3).
2.2.4. c(3),t(3)-Dimethyl-r(2),c(6)-di(4-bromophenyl)phenylpiperidin-4-one picrate (4)
Yield: 75%. m.p. 156-158°C; IR (KBr) (cm-1): 3091 (aromatic C-H), 1722 (C=O),
1619 (C=C), 1559 (NO2 asymmetric), 1438 (C-O), 1326 (NO2 symmetric), 1074 (C-N);
1H NMR (DMSO-d6, 400 MHz): δ (ppm): 10.14 (br s, 1H, Eq-NH), 9.58 (br s, 1H, Ax-NH),
8.60 (s, 2H, picryl ring), 7.70-7.68 (m, 4H, Ar-H), 7.72 (d, 2H, J = 8.4 Hz, Ar-H),
7.46 (d, 2H, J = 8.4 Hz, Ar-H), 4.95 (d, 1H, J = 12.4 Hz, H-6), 4.83 (br s, 1H, H-2), 3.61
(d, 1H, J = 14.8 Hz, H5a), 2.73 (d, 1H, J = 13.2 Hz, H5e), 1.19 (s, 3H, CH3), 0.93 (s, 3H,
CH3); 13C NMR (DMSO-d6, 100 MHz): δ (ppm): 206.04 (C=O), 160.83 (C-O), 141.72,
131.47, 131.25, 131.13, 130.87, 125.23, 124.48, 122.99, 122.48, 65.92 (C-2), 57.77 (C-6),
47.35 (C-5), 20.59 (CH3), 19.55 (CH3).
2.2.5. c(3),t(3)-Dimethyl-r(2),c(6)-di(4-methylphenyl)phenylpiperidin-4-one picrate (5)
Yield: 76%. m.p. 144-146°C; IR (KBr) (cm-1): 3075 (aromatic C-H), 1709 (C=O),
1613 (C=C), 1558 (NO2 asymmetric), 1440 (C-O), 1320 (NO2 symmetric), 1075 (C-N);
1H NMR (DMSO-d6, 400 MHz): δ (ppm): 10.15 (br s, 1H, Eq-NH), 9.23 (br s, 1H, Ax-NH),
8.59 (s, 2H, picryl ring), 7.49 (d, 2H, J = 7.6 Hz, Ar-H), 7.39 (d, 2H, J = 8.0 Hz, Ar-H),
7.29-7.27 (m, 4H, Ar-H), 4.89 (br s, 1H, H-6), 4.76 (br s, 1H, H-2), 3.63 (t, 1H, J = 14.4 Hz,
H5a), 2.66 (d, 1H, J = 15.2 Hz, H5e), 2.22 (s, 6H, CH3 at Ar ring), 1.19 (s, 3H, CH3), 0.92
(s, 3H, CH3); 13C NMR (DMSO-d6, 100 MHz): δ (ppm): 206.12 (C=O), 160.83 (C-O),
141.77, 129.00, 128.91, 128.73, 128.49, 125.18, 124.32, 66.42 (C-2), 58.23 (C-6), 47.56
(C-5), 20.69 (CH3), 20.62 (CH3 at Ar ring), 19.65 (CH3).

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2.2.6. c(3),t(3)-Dimethyl-r(2),c(6)-di(4-methoyphenyl)phenylpiperidin-4-one picrate (6)
Yield: 80%. m.p. 152-154°C; IR (KBr) (cm-1): 3090 (aromatic C-H), 1719 (C=O),
1623 (C=C), 1565 (NO2 asymmetric), 1432 (C-O), 1321 (NO2 symmetric), 1090 (C-N);
1H NMR (DMSO-d6, 400 MHz): δ (ppm): 10.06 (br s, 1H, Eq-NH), 9.27 (br s, 1H, Ax-NH),
8.59 (s, 2H, picryl ring), 7.54 (d, 2H, J = 8.4 Hz, Ar-H), 7.42 (d, 2H, J = 8.8 Hz, Ar-H),
7.03-7.00 (m, 4H, Ar-H), 4.88 (d, 1H, J = 12.8 Hz, H-6), 4.74 (br s, 1H, H-2), 3.78 (s, 6H,
OCH3 at Ar ring), 3.62 (d, 1H, J = 14.8 Hz, H5a), 2.65 (dd, 1H, J = 15.6 & 2.8 Hz, H5e), 1.19
13
(s, 3H, CH3), 0.91 (s, 3H, CH3); C NMR (DMSO-d6 100 MHz): δ (ppm): 206.72 (C=O),
160.85 (C-O), 160.10, 159.61, 141.74, 130.35, 130.22, 125.21, 124.40, 113.78, 113.60, 65.94
(C-2), 57.86 (C-6), 55.25 (OCH3 at Ar ring), 55.19 (OCH3 at Ar ring), 47.60 (C-5), 20.69
(CH3), 19.61 (CH3).
2.2.7. c(3),t(3)-Dimethyl-r(2),c(6)-di(4-benzyloxyphenyl)phenylpiperidin-4-one picrate (7)
Yield: 84%. m.p. 164-166°C; IR (KBr) (cm-1): 3143 (aromatic C-H), 1702 (C=O),
1619 (C=C), 1560 (NO2 asymmetric), 1436 (C-O), 1330 (NO2 symmetric), 1076 (C-N);
1H NMR (DMSO-d6, 400 MHz): δ (ppm): 10.08 (br s, 1H, Eq-NH), 9.23 (br s, 1H, Ax-NH),
8.60 (s, 2H, picryl ring), 7.53 (d, 2H, J = 8.8 Hz, Ar-H), 7.46-7.33 (m, 12H, Ar-H), 7.12-7.09
(m, 4H, Ar-H), 5.16 (s, 2H, OCH2), 5.14 (s, 2H, OCH2), 4.87 (br s, 1H, H-6), 4.74 (br s, 1H,
H-2), 3.58 (d, 1H, J = 11.2 Hz, H5a), 2.65 (d, 1H, J = 14.8 Hz, H5e), 1.19 (s, 3H, CH3), 0.91
(s, 3H, CH3);13C NMR (DMSO-d6, 100 MHz): δ (ppm): 206.14 (C=O), 160.85 (C-O),
159.05, 158.64, 141.78, 136.78, 136.76, 130.37, 130.22, 128.42, 127.88, 127.84, 127.65,
127.54, 125.21, 124.32, 114.71, 114.48, 69.22 (OCH2), 69.17 (OCH2), 65.91 (C-2), 57.85
(C-6), 47.61 (C-5), 20.70 (CH3), 19.61 (CH3).
3. Results and Discussion
3.1. Chemistry
The method used to synthesize the various substituted c(3),t(3)-dimethyl-r(2),c(6)-
diarylpiperidin-4-one picrates 1-7 is furnished in Scheme 1. The c(3),t(3)-dimethyl-r(2),c(6)-
diarylpiperidin-4-ones were obtained by the double Mannich condensation of various
substituted benzaldehydes, ammonium acetate, and isopropyl methyl ketone in the molar
ratio of 2:1:1 in ethanol medium at warm conditions, and kept at room temperature for 4 to 6
hrs. The piperidinium picrates 1-7 have been prepared by mixing equimolar solution of

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c(3),t(3)-dimethyl-r(2),c(6)-diarylpiperidine-4-ones and picric acid in ethanol and stirring the
solution continuously for 40 min. The physical data of the synthesised compounds 1-7 are
1
given in Table 1. The synthesized compounds have been characterised by IR, H NMR and
13C NMR spectral data.
From the IR spectra of piperidone picrates 1-7, it is inferred that the C=O peak
appeared between 1702 and1725 cm-1, the C=C stretching vibration between 1608 and 1623
cm-1 and the C-O stretching vibration between 1432 and 1440 cm-1. The IR spectra data are
summarized in Table 2. The IR spectrum of 2 is shown in Fig. 1.
Assignments were made based on the positions, integrals and multiplicities of the
1
signals in the H NMR spectra. The coupling constant values of J = ~12 Hz and J = ~3 Hz
due to large and small couplings of H(5)-H(6) in compounds 1-7 confirm the equatorial
orientation of all the substituents, similar to their corresponding parent piperidin-4-ones.
1
In the NMR spectra of compounds 1-7 in DMSO-d6, the benzylic proton H-2
appeared as a broad singlet at 5.48 ppm due to partial coupling with the NH protons. This is
because of the slow exchange of NH protons due to hydrogen bonding. The coupling
constants of compounds 1-7 could not be determined accurately, because the lines were broad
with poor resolution. In most of the cases, the determination of coupling constants of low
value involving neighboring axial and equatorial protons was not possible. Further, in case of
larger coupling constants J6a5a and J6a5e, NH could not be determined for want of data. The 1H
chemical shift values are given in Table 3.
It is inferred from Table 3 that for compounds 1-7 and from the 1H NMR spectrum of
compound 2 (Fig. 2) the chemical shift of benzylic proton H(2) appeared in the up field
region compared to the benzylic proton H(6), and it was attributed to the magnetic
anisotropic effect. Further, it has been reported that similar up field shift was observed for
the nearby axial proton by the introduction of equatorial substituent [7].
In the piperidin-4-one ring, because of protonation, all the protons were remarkably
deshielded whereas all the carbons were shielded. The effect on C(2), C(3), C(5) and C(6)
was due to the polarization of C-H bonds i.e., the protons acquired a partial positive charge
and carbon a partial negative charge. It is interesting to note that proton H(5e) appeared in the

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up field region, compared to H(5a) i.e., δeq-δax was negative. The axial hydrogen at C-5, H(5a)
and C-3, CH3 present in the protonated piperidone derivatives had severe syn-1,3-diaxial
interaction with axial NH bond. Due to these interactions, carbons were shielded and protons
deshielded to a large extent (Fig. 3).
It is also observed in the protonated piperidone derivatives that the benzylic protons
i.e., H-2 and H-6, were deshielded more than protons at H-5, and the benzylic carbon was
shielded less than C-3 and C-5 carbons. These were due to the magnetic anisotropic effect of
the additional axial NH bond and the change in the electronegativity of nitrogen.
When the piperidone derivatives were protonated, the polarity of C=O group
decreased due to the electrostatic effect of the nitrogen atom bearing a positive charge, which
in turn reduced the positive charge of the carbonyl carbon. Due to this the carbon got shielded
and appeared at 206 ppm in its 13C NMR spectra.
13
The C NMR spectra of the compounds 1-7 were recorded, and the chemical shift
values are reproduced in Table 4. It clearly indicates that all carbons were shielded due to
protonation. The magnitude of deshielding observed on C(2) and C(6) carbon is found to be
higher than that on C(3) and C(5) carbon due to protonation and severe syn-1,3-diaxial
interaction of the axial NH bond with the axial hydrogen at C(5) and axial methyl group at
C(3). Because of these reasons, the axial methyl proton at C(3) and H(5a) proton were
deshielded, whereas the corresponding carbons were shielded.
3.2. Energetic properties
3.2.1. Oxygen balance (OB% or ꢀ)
Oxygen balance is an indicator used to determine the extent to which an explosive can
be oxidized. If an explosive contains sufficient oxygen to convert all the carbon, hydrogen
and the metals present in it to carbon dioxide, water and metal oxide respectively, with no
excess oxygen present, the molecule is said to have a zero oxygen balance. If it contains more
oxygen than needed, then it is said to have a positive oxygen balance; if it contains less
oxygen than needed, then the explosive is said to possess a negative oxygen balance [8]. It is
an important parameter to decide on the performance of high energetic materials.

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The nature of the gases released during an explosion is provided from its oxygen
balance value. If an explosive has a large and negative value, it suggests that toxic gases like
carbon monoxide will be liberated, which is not conducive to the production of commercial
explosives. If the oxygen balance is large and positive, toxic gases such as NO, NO2 are
liberated. The liberated toxic gases must be of minimum quantity. If the oxygen balance is
zero, i.e., if it is balanced, then water, carbon dioxide, and nitrogen are the detonation
products [9].
The oxygen balance for ammonium nitrate is +20 and that of TNT is -74, and mixing
these two in an appropriate proportion will lead to zero oxygen balance and result in the
mixture acquiring explosive properties [10]. Oxygen balance also influences the sensitivity,
strength, and brisance of an explosive.
The oxygen balance of the synthesized high energy materials is calculated using the
formula
H
2
M − O
+
−100 × MW (O) × 2C +
OB =
MW (explosive)
--------------------------------------------------------------(1)
Or by an alternate method for an explosive with molecular mass M and having a
general formula CaHbNcOd.
d−(2a)-b/2
×
1600
OB (Ω) =
MW (explosive)
---------------------------------------------------------------------(2)
The oxygen balances of the synthesized compounds are similar to those of the
reference compounds, picric acid and Dunnite. The synthesised compounds have large
negative values, which show that these compounds would liberate a large amount of
obnoxious gases such as carbon monoxide.
3.2.2. Crystal density
Crystal density is important to determine the detonation performance of high
energetic materials. To study the performance of explosive properties like detonation
pressure, detonation velocity, energy output, and gurney velocity of explosives, the

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determination of crystal density is of utmost importance
[11]. Crystal density may be
calculated for nitro aromatic energetic compounds with the general formula CaHbNcOd by
a
Mw
b
Mw
c
Mw
d
Mw
ρο
= 10.57
+ 0.1266
30.38
35.18
+
+
---------------------(3)
where ρ0 is the core crystal density and, Mw the molecular weight of energetic materials.
Density is an important property in explosive selection. Density below 1.0 g/cm3 means
that the explosive may float in water. Increasing the density leads to increasing the
velocity of detonation (VoD) and detonation pressure. A higher density for non-ideal
explosive risks dead pressing (making the material hard to ignite, and if ignited, burn
without detonation).
From the data on the synthesized compounds, it is inferred that their crystal density
was less than that of our reference material picric acid and Dunnite. Compound
6
possesses the highest core crystal density, and compound
density.
4 containing bromine the lowest
3.2.3. Heat of formation (Condensed Phase)
The “energy content” of an energetic compound is determined by its heat formation. It
plays a vital role in designing new energetic materials or evaluating the existing ones, while
investigating its characteristics. Heat formation is helpful to determine the detonation
temperature, energy output, gurney velocity of explosives etc. Keshavarz gives a generalised
equation to calculate the heat formation of condensed phase for energetic materials
containing CaHbNcOd as [12, 13].
∆Hf(c) (kcal mol-1)
− 22.38n
− 15.56n
= 7.829a − 8.117b + 16.52c − 27.80d + 29.82n
Ar-NH
OH
NO2
+ 53.34n
− 48.34n
+ 29.02n
−N=N−
+ 3.241(n −1)
COOH
cyclo N−O−N
Ar
----------------------------(4)
where nNO2, nOH and nCOOH are the number of nitro, hydroxyl and carboxylic groups,
nAr-NH is the number of NH or NH2 functional groups attached to aromatic rings, and the
condensed phase of heat of formation is represented by ∆Hf(c).

11
ACCEPTED MANUSCRIPT
The heat formation of synthesized compounds 1-7 is on a negative scale. Compound
3
, which contains chlorine, has the value -60.66 kcal/mol and has more capacity for heat
formation than picric acid.
3.2.4. Heat of detonation
The amount of energy released during detonation and the rate of its release decide the
performance of an energetic compound. The difference between the heat formation of
detonation products and that of the explosive formulation divided by the weight of the
explosive gives the heat of detonation. Keshavarz gives a new approach to estimate the heat
of detonation of aromatic energetic compounds, which is expressed as
Q(kJ/g) = 2.129 + 0.178c + 0.874r + 0.160r + 0.965CSFG
d/a
b/d
---------------------------------(5)
where rd/a is the ratio of oxygen to carbon and rb/d the ratio of hydrogen to oxygen atoms and
CSFG = -1 that of aromatic energetic compounds having specific functional groups [14,15].
The calculated heat of detonation of the synthesised compounds is less than that of the
reference materials, and among the synthesized compounds, compound
substituent possesses high heat of detonation (2.69 kJ/g).
5 with a methyl
3.2.5. Velocity of Detonation
The rate of propagation of a shockwave in an explosive is called the velocity of
detonation (VoD). It directly depends upon the density of the given explosive and not
influenced by external factors. It can be calculated by using two reliable formulae, and the
VoD for the synthesized compound is calculated and tabulated.
nO + nN − (nH/2nO) + (A/3) − (nB/1.75) − (nC/2.5) − (nD/4) − (nE/5)
F = 100 ×
− G
MW
--(6)
F − 0.26
D =
0.55
-------------------------------------------------------------------------------------------(7)
where nB is in excess of the number of oxygen atoms that are already available to
form CO2 and H2O, nC is the number of oxygen atoms connected to carbon by means of a

12
ACCEPTED MANUSCRIPT
double bond, nD the number of oxygen atoms connected to carbon by means of a single bond
and nE the number of nitro groups as nitrate ester or as nitric acid salt. In the case of an
aromatic compound A = 1; otherwise A = 0. For a liquid explosive G = 0.4 and for a solid
explosive G = 0, F is the detonation factor, and D the detonation velocity [16-18].
It can also be calculated using the formula for an explosive containing CaHbNcOd
D(km/s) = 1.644 + 3.593ρ0 − 0.132a − 0.0034b + 0.120c + 0.0442d − 0.2768n
NRR' -------(8)
where nRR´ is the number of specific groups including NH2, NH4, and cyclic N-N-N groups.
Higher values of crystal density provide higher values of detonation velocity. For a
high explosive, the VoD ranges from 2.74 km/s to over 8.38 km/s [17]. For the newly
synthesized compounds, the VoD ranges from 2.52 to 3.89 km/s, showing that the presence
of benzyloxy group reduces the VoD (2.69 km/s) and the presence of highly electronegative
fluorine has high value of VoD (3.89). This is because fluorine is the best oxidizer, and the
introduction of fluorine increases the energy and density. Out of the seven compounds, five
compounds 1, 2, 3, 5 and
6 possess the VoD of more than 2.74 km/s showing that they are
high explosives.
3.2.6. Detonation pressure
The measurement of shock waves transmitted into water by the detonation of the
cylindrical explosive charges of a standard size give the detonation pressure. It is denoted as
Pd.
Pd estimation for commercial explosive is:
Pd = 0.25 × VoD2 ×
ρ
----------------------------------------------------------------------------------(9)
It can also be calculated for the energetic compounds containing CaHbNcOd using the
formula below [19].
P(kbar) = 22.32 + 104.0ρ02 − 10.98a − 1.997b + 5.562c + 5.539d − 23.68n − 154.1n0
1
NHx
-----------------(10)

13
6, which contains the methoxy group, possesses the highest pressure
ACCEPTED MANUSCRIPT
Compound
(22.11 kbar) among the synthesized compounds, and compound
group has the lowest pressure (2.02 kbar).
7 which contains benzyloxy
3.2.7. Gurney Energy
The amount of specific energy liberated during the detonation of a given
explosive is called gurney energy. Keshavarz et al. introduced a correlation to find gurney
energy using the condensed phase of heat formation [20].
7.543a + 2.676b + 31.97c + 35.91d − 0.196 ∆Hf (c)
0.5
ρο
√2E = 0.227 +
MW
---------------(11)
4 which contains bromine has the lowest gurney energy of 0.74 km/s.
Compound
3.2.8. Sensitivity
The ease with which an explosive can be ignited or detonated is called the sensitivity
of an explosive, i.e., the amount and intensity of shock, friction, or heat that are required.
Sensitivity is of three types:
•
Impact-sensitivity is indicated as the distance through which a standard weight
must be dropped onto the material to cause it to explode.
Friction-sensitivity is indicated by what occurs when a weighted pendulum
scrapes across the material (it may snap, crackle, ignite, and/or explode).
Heat-sensitivity is indicated in terms of the temperature at which flashing or
explosion of the material occurs.
•
•
3.2.8.1. Impact sensitivity
Impact sensitivity is measured experimentally by subjecting the synthesized materials
to the impact of a standard weight falling from various heights and recording the occurrence
or absence of reaction. A height of 50% probability in causing an explosion h50 is measured
by impacting the sample with a falling hammer, typically of 2.5 kg weight. It can be
measured by using the formula [21].
46.29a + 35.63b − 7.701c + 7.942d + 44.42n
+ 102.3n
−CNNC
−
−CNC−
log h50 =
Mw
------------(12)

14
ACCEPTED MANUSCRIPT
where n-CNNC-and n-CNC- are the numbers of -CN-NC- and–CNC- moieties respectively in the
molecule. Compound (15283 cm), which has a methyl substituent, is more insensitive than
5
the reference materials picric acid and Dunnite. Normally, the synthesized compounds
possess less impact sensitivity, which shows that the compounds are stable.
3.2.9. Explosive power
Explosive power is the measure of the ability of energetic materials to do work or the
amount of heat given off at constant volume. It is also called as the strength or potential of
the explosive. The strength is measured in comparison with TNT, which is a standard
explosive [22]. A simple reliable method to evaluate the power is given as
EP(%TNT) = 113.0 − 5.16a + 2.786c + 3.612d − 46.18OCF
----------------------------------(13)
where OCF is the correctional function. This correlation co-efficient is equal to 0.80,
which is proved relatively good, as there is uncertainty in the determination of power, when
theoretical and experimental values are high. The explosive power of trinitroimidazole picrate
is the maximum with 98.86, in a TNT scale of 100.
Taking the parameters mentioned above into consideration, the performance of the
energetic materials is calculated, and from the values, all the synthesized compounds are
found to have less explosive power than the reference material. Compound 6, which contains
methoxy group with more oxygen has the highest explosive power of 124.92, close to that of
picric acid with a value of 131.45.
3.2.10. Power index
Power index is the ratio between the explosive power value of the explosive and the
explosive power of a standard explosive (picric acid) [23].
QV
× 100
Power index =
Q(picric acid) V(picric acid)
--------------------------------------------------(14)
Here the data for Q(picric acid) and V(picric acid) are 3250 kJ/g and 0.831 dm3 respectively.
From the synthesised compounds, compound
possesses the highest strength.
6 (Table 5) has the highest power index, as it

15
ACCEPTED MANUSCRIPT
4. Conclusions
Seven piperidone picrates 1-7 were prepared and characterized by spectral data. The
NMR spectral studies suggest that the piperidone picrates existed in chair confirmation with
all substituents in equatorial orientation. The picrate anion influenced the rest of the molecule
in such a way that the chemical shift of heterocyclic ring protons was deshielded, whereas
carbons were shielded. The physical and explosive properties of the synthesized compounds
are calculated with the standard equations and compared with those of LOTUSES code
simulated results. Among the synthesized compounds, five compounds (1-3, 5 and 6) have
the VoD of high explosives, and they are thermodynamically stable, and the risk involved in
handling high explosives is mitigated. The results of this paper may be helpful in designing
and developing an ideal energetic compound in the near future.
Supplementary material
Supplementary data to this article can be found online version.
References
[1] H. Muthurajan, R. Sivabalan, M.B. Talawar, M. Anniyappan, S. Venugopalan, Prediction
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LUMO and NLO properties of 3t-pentyl-2r,6c-diphenylpiperidin-4-one picrate based on
DFT calculations, J. Mol. Struct. 1105 (2015) 225-237.
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[5] U.P. Singh, N. Goel, G. Singh, P. Srivastava, Supramolecular architecture of picric acid
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24 (2012) 285-297.

16
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[6] N. Goel, U.P. Singh, Syntheses, structural, computational, and thermal analysis of acid-
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piperidine,Tetrahedron 24 (1968) 279-287.
[8] J. Akhavan, The Chemistry of Explosives, third ed., The Royal Society of Chemistry,
United Kingdom, 1998.
[9] H. Muthurajan, R. Sivabalan, M.B. Talawar, S. Venugopalan, B.R. Gandhe, Computer
code for the optimization of performance parameters of mixed explosive formulations,
J. Hazard. Mater. 136 (2006) 475-481.
[10] R. Meyer, J. Köhler, A. Homburg, Explosives, sixth ed., Wiley-VCH & Co. KGaA,
Weinheim, 2007.
[11] N. Zohari, M.H. Keshavarz, S.A. Seyadsadjadi, Some high nitrogen derivatives of
nitrotetrazolyl imidazole as new high performance energetic compounds, Cent. Eur. J.
Energ. Mater. 11 (2014) 349-362.
[12] M.H. Keshavarz, A simple procedure for calculating condensed phase heat of formation
of nitroaromatic energetic materials, J. Hazard. Mater. 136 (2006) 425-431.
[13] T.M. Klapotke, Chemistry of High energetic materials, second ed., Walter de Gruyter
GmbH & Co, KG, Berlin, 2012.
[14] R.A. Sickler, Explosive principles: An essential guide to understanding explosives and
detonations, Paladin press, USA, 1992.
[15] M.H. Keshavarz, Predicting heats of detonation of explosives via specified detonation
products and elemental composition, Indian J. Eng. Mater. Sci. 14 (2007) 324-330.
[16] L.R. Rothstein, Predicting high explosive detonation velocities from their composition
and structure (II), Propellants Explos. Pyrotech. 6 (1981) 91-93.
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prediction of performance and thermodynamic parameters of high energy materials,
J. Hazard. Mater. 112 (2004) 17-33.

17
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[19] N. Kubota, Propellants and Explosives: Thermochemical aspects of combustion, Wiley-
VCH, GmbH, Weinheim, Germany, 2002.
[20] M.H. Keshavarz, H. Motamedoshariati, R. Moghayadnia, H.R. Nazari,
J. Azarniamehraben, A new computer code to evaluate detonation performance of high
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1218-1228.
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[23] M. Berthelot, W. Macnab, C.N. Hake, Explosives and their power, Wentworth press,
Miami, Florida, 2016.

18
ACCEPTED MANUSCRIPT
Figures and Scheme captions
Fig. 1. IR spectrum of
Fig. 2.1H NMR spectrum of
Fig 3. Schematic representation of syn-1,3-diaxial interactions.
Fig. 4.13C NMR spectrum of
Scheme 1. Synthetic route for c(3),t(3)-dimethyl-r(2),c(6)-diarylpiperidin-4-one picrate
derivatives 1-7
2.
2
.
2
.
.

ACCEPTED MANUSCRIPT
23
Table 1
Physical data of the compounds 1-7.
Compound M.p. (°C)
Yield (%)
Molecular
formula
Elemental analysis (%)
C
H
N
Found
(Calcd)
59.00
Found
(Calcd)
4.86
Found
(Calcd)
10.95
158-160
141-143
148-150
156-158
144-146
152-154
164-166
82
79
86
75
76
80
84
C25H24N4O8
1
2
3
4
5
6
7
(59.05)
(4.76)
4.27
(11.02)
10.16
(10.29)
9.50
C25H22F2N4O8 55.55
(55.15)
(4.07)
3.95
C25H22Cl2N4O8 52.23
(52.01)
(3.87)
3.56
(9.70)
8.21
C25H22Br2N4O8 45.27
(45.07)
(3.33)
5.56
(8.41)
10.77
(10.44)
7.98
C25H24N4O8
C27H28N4O8
C39H36N4O10
60.77
(60.44)
57.24
(5.26)
4.99
(57.04)
64.52
(4.96)
4.92
(7.77)
10.06
(9.85)
(64.99)
(5.03)

ACCEPTED MANUSCRIPT
24
Table 2
IR Spectral data (cm-1) of the compounds 1-7.
1
2
3
4
5
6
7
Assignment
3175
1719
1160
1609
1437
1568
1319
3075
1725
1161
1608
1435
1560
1318
3092
1723
1085
1611
1439
1563
1317
3091
1722
1074
1619
1438
1559
1326
3075
1709
1075
1613
1440
1558
1320
3090
1719
1090
1623
1432
1565
1321
3143
1702
1076
1619
1436
1560
1330
C-H
C=O
C-N
C=C
C-O
NO2 asymmetric stretching
NO2 symmetric stretching

ACCEPTED MANUSCRIPT
25
Table 3
1H Chemical shifts (ppm) of compounds 1-7.
Compound H(6)
H(2)
H(5a)
H(5e)
Ax-
NH
9.40
Eq-
NH
CH3 at
C-3
OCH2
-
OCH3 CH3
Picryl Aromatic protons
ring
4.99
(br d)
4.98
(d)
4.87
3.64
(t)
2.74
(dd)
2.72
(dd)
10.23 0.94 (s)
(br s) &1.21 (s)
10.19 0.93 (s)
-
-
-
-
8.60
7.48-7.53 (m) &
7.63- 7.65 (m)
7.29-7.35 (m),
7.54 - 7.58 (m)
&7.67-7.70 (m)
7.48-7.57 (m) &
7.64 (d)
1
2
(br s)
4.87
(br s)
9.43
(s)
3.64
( t)
-
8.60
(s)
(br s)
(br s)
(br s)
&1.21 (s)
4.96
(d)
4.84
3.61
( d)
3.61
(d)
2.73
(dd)
2.73
(d)
9.56
9.59
0.93 (s)
-
-
-
-
-
-
-
-
-
8.59
(s)
3
4
5
6
7
(br s)
4.83
(br s)
9.58
(br s)
&1.19 (s)
4.95
(d)
10.14 0.93 (s)
(br s) &1.19 (s)
10.15 0.92 (s)
(br s) &1.19 (s)
10.06 0.91 (s)
(br s) &1.19 (s)
10.08 0.91 (s)
(br s)
8.60
(s)
7.46 (d), 7.72 (d)
&7.68-7.70 (m)
7.27 -7.29 (m),
7.39 (d) & 7.49 (d)
7.00-7.03 (m),
7.42 (d) &7.54 (d)
7.09-7.12 (m),
7.33-7.46 (m)
&7.53 (d)
(br s)
4.76
(br s)
9.23
4.89
(br s)
4.88
(d)
3.63
(t)
2.66
(d)
2.22
(s)
-
8.59
(s)
(br s)
4.74
(br s)
9.27
3.62
( d)
3.58
( d)
2.65
(dd)
2.65
(d)
3.78
(s)
8.59
(s)
(br s)
4.74
(br s)
9.23
4.87
(br s)
5.14 (s) -
-
8.60
(s)
(br s)
(br s)
&1.19 (s) & 5.16
(s)

ACCEPTED MANUSCRIPT
26
Table 4
13C Chemical shifts (ppm) of compounds 1-7.
Compound C(2)
C(3)
C(5)
C(6)
OCH2
CH3at C-3 C=O
CH3
-
OCH3
-
C-O
Aromatic
Carbons
66.46
65.74
Merged
with
DMSO-d6
Merged
with
47.42 58.29
47.45 57.67
-
-
19.67 &
20.74
206.13
160.82 124.29-
141.79
1
2
19.54 &
20.60
206.19
-
-
160.83 115.22 -
141.73,
DMSO-d6
162.31 &
162.65
71.09
65.92
66.42
65.94
65.91
Merged
with
DMSO-d6
Merged
with
DMSO-d6
Merged
with
DMSO-d6
Merged
with
52.65 62.96
47.35 57.77
47.56 58.23
47.60 57.86
-
-
-
-
24.79 &
25.83
211.34
206.04
206.12
206.72
206.14
-
-
-
-
166.08 129.71 –
146.97
3
4
5
6
7
19.55 &
20.59
-
160.83 122.48 –
141.72
19.65 &
20.69
20.62
160.83 124.32 –
141.77
19.61 &
20.69
-
-
55.19
&
55.25
-
160.85 113.60 –
160.10
DMSO-d6
Merged
with
47.61 57.85 69.17
19.61 &
20.70
160.85 114.48 –
159.05
&
DMSO-d6
69.22

ACCEPTED MANUSCRIPT
27
Table 5
Energetic properties of compounds 1-7.
Properties
1
2
3
4
5
6
7
Picric acid Dunnite
Oxygen balance
-169.91
1.32
-155.75
1.23
-146.87
1.16
-127.65
1.01
-178.92
1.29
-163.23
1.34
-190.92
1.24
-43.39
1.74
-52.00
1.72
Crystal density
(g/cm3)
Heat of formation in -89.81
solid phase (kcal/mol)
-70.08
2.59
-60.66
2.59
-70.08
2.59
-110.45
2.69
-151.68
2.65
-117.06
2.68
-58.21
4.03
-70.75
3.84
Heat of detonation
(kJ/g)
2.64
Velocity of detonation 3.40
(km/s)
3.89
2.98
2.52
3.11
3.66
2.69
7.56
7.58
Detonation pressure
(kbar)
14.91
12.85
1730.1
1.04
11.97
1736.0
1.15
10.03
1730.7
0.74
11.88
1470.0
1.15
22.11
1686.9
1.23
2.02
83.01
4915.1
1.95
84.46
3830.9
2.03
Detonation
1628.7
1.18
1452.4
1.04
temperature (K)
Gurney energy
(km/s)
Impact sensitivity
(cm)
7643.5
113.31
118.00
2511.5
93.76
97.66
1607.6
108.98
113.52
600.3
64.30
66.98
15283
112.21
116.88
9752
10656
106.65
111.09
65.9
358.5
139.19
144.9
Power relative to
TNT as standard 100
Power index (%)
124.92
130.12
131.45
136.9

19
ACCEPTED MANUSCRIPT
Fig. 1.

20
ACCEPTED MANUSCRIPT
Fig. 2.
Fig 3.

21
ACCEPTED MANUSCRIPT
Fig. 4.

22
ACCEPTED MANUSCRIPT
O
C
CH3
CH3
H3C
O
CH3
CH3
CHO
CHO
R
EtOH warm
+
N
H
R
R
NH4OAc
R
OH
O2N
NO2
EtOH
Stirring, RT
Compounds
R
H
1
NO2
Picric acid
F
2
3
4
5
6
O
CH3
Cl
Br
CH3
N
O
H
H
R
R
Me
O2N
NO2
OMe
OCH2Ph
7
NO2
1-7
Scheme 1.